If the price of a commodity increases by R%, then the reduction in consumption so
as not to increase the expenditure is R X 100 %100 + R
If the price of a commodity decreases by R%, then the increase in consumption so
as not to decrease the expenditure is R X 100 %100 - R

Results on Population : Let the population of a town be P now and suppose it
increases at the rate of R% per annum, then :
1. Population after n years =
= P (
1 + R/100
)n
2. Population n years ago = = P P (
1 + R/100
)n

Results on Depreciation : Let the present value of a machine be P. Suppose it
depreciates at the rate of R% per annum. Then :
1. Value of the machine after n years =
= P (
1 - R/100
)n
2. Value of the machine n years ago = = P P (
1 - R/100
)n

If A is R% more than B, then B is less than A by R X 100 %100 + R
If A is R% less than B, then B is more than A by R X 100 %100 - R